1. FIELD OF THE INVENTION
The present invention relates to a method of treating lumpy biological products, which products are subjected to a thermal treatment, an expansion to vacuum conditions and a drying at vacuum conditions.
2. DESCRIPTION OF THE PRIOR ART
According to the known methods the drying of lumpy vegetable and fruit products use is made of the so-called puffing or of the expanding in order to support the drying. Thereby, an expansion is made from an over-pressure of several bar (1 bar =14.5 psi) down to atmospheric pressure. Hereby a structural change occurs because the opened cells collapse. The products thus display a harder and tougher structure.
A plant is known, in which an expansion is made from atmospheric pressure down to a vacuum. It is, however, foreseen to effect a moistening by means of water vapor together with the thermal treatment. It, hereby, has been found to be a drawback that the state of the vacuum is reached only very slowly, wherewith a pressure equalization and conclusively a too low pressure gradient occurs.